Figure 1.

The process of malignant transformation. Cancer is a multi-staged procedure in which cells gradually acquire malignant characteristics. Initiation includes certain genetic/epigenetic changes resulting in the deregulated control of processes, such as cell-cycle progression, apoptosis, and proliferation. The clonal expansion of the initiated cell, which exhibits defective apoptosis, abnormal cell-cycle arrest, and excessive proliferation, leads to the formation of a preneoplastic lesion of closely attached cells. During progression, the genetically unstable preneoplastic cells progressively accumulate novel, malignant-related properties, such as the ability to escape from immune surveillance, migrate and invade new tissues, and form new tumors.